Natural Control of Root Diseases in Greenhouse Vegetable and Ornamental Crops

Due to concerns about environmental and human health, the use of chemical crop protection products is increasingly restricted. As a result, growers must seek alternatives, such as biological crop protection. However, options are still relatively limited, says Marta Streminska, microbial ecology researcher at WUR.

“There are no good alternatives yet for many chemical products, and growers are still searching. One possible approach is the use of biorationals — a broad category of naturally derived products, including micro-organisms. These products can be used to prevent disease but also to enhance the plant’s natural resistance.”

Root Diseases Caused by Fungi

In this project, Streminska and her colleagues investigated the effective use of biorationals in preventing infections of Fusarium, a fungus that causes root diseases. “We chose two cultivation systems: cucumber on rockwool and lisianthus — a cut flower — in soil. Fusarium is a major threat in both cases, though the systems differ significantly in substrate, environmental temperature, and irrigation practices. The species of Fusarium also differ: cucumber is primarily affected by Fusarium oxysporum f.sp. radicis-cucumerinum, while lisianthus is mainly affected by Fusarium f.sp. eustomae and Fusarium solani.”

Adding Micro-Organisms

The researchers initially focused on preventing infections using microbe-based products, says Streminska. “The idea is to introduce these micro-organisms in the hope that they establish themselves in the root zone — the rhizosphere — and protect the plant. For lisianthus, this worked fairly well with some biofungicides, but for cucumber, it was less successful. These micro-organisms often do not naturally occur in rockwool and may have difficulty establishing themselves in such a water-rich, low-organic environment. This led us to explore how we could support and manipulate the micro-organisms already naturally present around the roots in such systems.”

Greater Resistance Through Spent Mushroom Compost Tea

Streminska explains the next step. “We added spent mushroom compost tea to the nutrient solution. This tea strengthens and promotes specific groups of beneficial micro-organisms in the root zone, helping to prevent fungal infections. This method proved to be very effective for cucumber. It’s the first time that a cultivation trial has shown that resistance to root diseases in rockwool systems can be enhanced by manipulating the natural microbiome, such as through the use of mushroom compost tea. This is a valuable insight for developing more resilient cropping systems.”

Basis for Further Research

According to Streminska, the project has significantly increased our understanding of the role of micro-organisms in preventing Fusarium infections in greenhouse systems.

“We’ve only tested a limited number of additives so far, but there are likely many more ways to steer the natural microbiome in a growing medium to increase resistance to root diseases. Further research could examine what exactly happens in recirculating systems and whether the tested additives also affect disease control in other growing media — including organic substrates — used in the cultivation of fruiting vegetables.”

This research project was initiated by the Club of 100, a collaboration between Wageningen University & Research, BU Greenhouse Horticulture and suppliers in the greenhouse sector. The project was co-funded by the Top Sector Tuinbouw & Uitgangsmaterialen.